Recovery of liquid hydrocarbon fuels from waste plastics

Abstract

Plastics are non-biodegradable polymers of mostly containing carbon, hydrogen, and few other elements such as chlorine, nitrogen etc. Due to its non-biodegradable nature, the plastic waste contributes significantly to the problem of Municipal Waste Management. The production of plastics is significantly growing. Nowadays the plastic production is more than 200MT worldwide annually. According to a nation wide survey, conducted in the year 2004, approximately 10,000 tones (ten thousand tones) of plastic waste were generated every day in our country (India), and only 60% of it was recycled, balanced 40% was not possible to dispose off. So gradually it goes on accumulating, thereby leading to serious disposal problems. Plastic is derived from petrochemical resources. In fact these plastics are essentially solidified oil. They therefore have inherently high calorific value. Waste Plastics are mostly land filled or incinerated; however, these methods are facing great social resistance because of environmental problems such as air pollution and soil contamination, as well as economical resistance due to the increase of space and disposal costs. In a long term neither the land filling nor the incineration solve the problem of wastes, because the suitable and safe depots are expensive, and the incineration stimulates the growing emission of harmful and greenhouse gases e.g. NOx, SOx, COx etc. Accordingly, recycling has become an important issue worldwide. This method can be classified as energy recovery, material recycling and chemical recycling. Among them one of the prevalent alternative methods is the production of converted fuel and chemicals by means of the thermal or catalytic degradation of polymers. The main objective of this study was to investigate the effect of catalyst amount, reaction temperature, plastic type (especially HDPE) and weight ratio of waste plastic to catalyst, with a semi-batch reactor, based on the results of yields and yield distributions of liquid product as a function of lapsed time. And to study the product yields and their distribution with different types of catalysts (Silica- Alumina, Activated Carbon, Mordenite) in the catalytic degradation of waste plastics with respect to time and temperature. And also for finding the effect of particle size and structure of the catalyst on product distribution and yield. One more objective is quantitative analysis of gaseous, liquid and solid products from thermal and catalytic degradation of HDPE and the comparison of the physical properties of the liquid products and to suggest the best reactor design along with the economical factors effecting the commercialization of this technique. We have studied extensively the catalytic nature of HDPE both under catalytic and noncatalytic methods with the application of some important suitable catalysts, and about the catalyst characterization by the application of SEM and XRD. The cracking temperature of HDPE was very when compare with other plastics as we have observed from the literature. It was minimum 460ºC. we have reached better yield (76%) of liquid products with the application of Mordenite catalyst at this temperature. But, the time taken for the completion of the reaction was very high about one hr. The yield and the composition of the liquid product vary along with feed to catalyst ratio and reaction temperature. And all the liquid products we got were analyzed for their physical properties. The specific gravities of all the samples were existed in the range of gasoline and diesel range of fuels. We have also tested pour point, flash point and fire point. These were varied along with their individual composition.